The catalytic converters, especially three-way catalysts, used in combination with modern gasoline engines have resulted in a great reduction in tailpipe emissions of carbon monoxide, hydrocarbons and NOx. There is an increasing emphasis on fuel efficiency and diesel engines have an efficiency advantage over gasoline engines. Unfortunately, diesel engines are “lean burn” engines and their exhaust has very high levels of oxygen. These high levels of oxygen render gasoline catalytic converters useless for NOx reduction. Catalysts or catalytic systems that have been utilized for lean burn engines to date suffer from low removal of NOx, low thermal stability and a limited temperature window of operation. Most current catalytic systems for lean burn engines only achieve 7–12% NOx reduction as a passive system and 25–40% when supplemental hydrocarbon reductant is injected into the exhaust stream. Use of a non-thermal plasma system for reduction of NOx in conjunction with a particulate trap is disclosed in U.S. Pat. No. 6,038,854 issued Mar. 21, 2000 to Penetrante et al.
The present invention is directed to overcome one or more of the problems as set forth above.